Effective environmental sampling strategies for monitoring Legionella spp contamination in hot water systems

Abstract

The prevention and control of legionellosis in hospital settings involves environmental sampling, among other measures. The data yielded by sampling constitute an important means of risk assessment and provide a valid basis on which to plan remedial (cleansing and disinfection) and preventive (maintenance) interventions. This retrospective study had 2 objectives: (1) to evaluate the utility of biofilm sampling at distal sites and (2) to identify an efficient environmental sampling strategy. Samples of hot water and biofilm were collected between June 1999 and March 2008 from 41 hospitals in Italy's Piemonte region. We analyzed results of the samples (water and biofilm) taken from the same site and results of the water samples taken from the recirculation loop and water samples taken from the distal sites during the same sampling run. Microbiological analysis was performed on 3910 pairs of samples (water/biofilm). In 81% of the pairs, the results were concordant; in 17% of the pairs, Legionella was isolated only from the water samples, and in only 2% of the pairs was Legionella isolated from the biofilm sample alone. Data from 299 sampling runs show that 79% (236) of results from the water samples taken from the recirculation loop and water samples taken from the distal sites during the same sampling run were concordant, and 21% (63) were discordant. Our findings suggest that hospitals could safely adopt a simpler (water sampling only without biofilm sampling) and more efficient (monitoring of the entire system through sampling of recirculation loop water) environmental sampling policy.